Hi Susan, Your response makes it much clearer. Sorry about the "Ferrites 101" in my previous response. Hope I didn't insult your intelligence.
Now that I see the true nature of your question, I only have one tidbit to offer from experience. In one telecom circuit we had (starting from the connector): A ferrite bead, a 1206 zero ohm resistor (used as a jumper where a current limiting resistor could be placed) a fuse (1.25A, fast acting), a sidactor (across from one line to the other, not to ground). In this application, the ITU K.20 and ITU K.21 lightning pulses blew the 1206 ferrite chips off of the board before the fuses would activate. This also happened to a MOV which we had originally used; that's why we ended up with a sidactor. The ferrite chips were rated for 150mA steady state. I, like you, was unsure of their pulse current capability. I could find no specification for it in the ferrite data sheets. The fact that they disintigrated gave us some idea that they were probably a little under-rated. We replaced them with PREM part number SPG-104 (a multi-turn bead on a lead part with higher current rating). These parts worked. These parts had a steady-state current rating similar to the in-line fuse. Coincidence? Maybe. So, in our case....yes our lightning pulse did "alter the properties of the ferrite" (and how). I know that you have a different circuit and a different lightning requirement; so take my advice with a grain of salt (as always). I hope that you can find some bit of information there that you can extrapolate to your situation. Chris > -----Original Message----- > From: shbe...@rockwellcollins.com [SMTP:shbe...@rockwellcollins.com] > Sent: Wednesday, June 05, 2002 1:09 PM > To: emc-p...@ieee.org > Subject: RE: ferrite transient voltage/current response > > > > Sorry that I wasn't clear; I typically try to keep my questions general so > not to get too detailed about the specific application. And thanks to Bob, > Chris and Mike who have responded ... putting it into Chris's words ... I > was just trying to find out if ferrites had ratings to prevent them from "j > ust plain blowing the ferrite to smithereens". Also, I was looking for a > shortcut if someone else had faced this question rather than reading > through all of the vendor web sites. > > I understand and have used ferrites quite often for typical EMI > suppression; the ferrites typically being rated for the application > currents, voltages, etc. In this case, the program is trying to protect a > power supply input from the DO-160 waveform 5B pin injected lightning pulse > of 300 volts open circuit & 300A short circuit. If the Gas Discharge Tube > is located past (closer to the supply which was done for packaging > limitations) than the "T" EMI filter, a question was raised as to whether > the ferrite properties would be altered by the lightning pulse. Most of > the standard literature on the use of ferrites does not address these types > of transients. > > > Susan Beard > ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on "browse" and then "emc-pstc mailing list"
